Rotating sorters or sizers, commonly called trommels, are well known in the art of classifying grains, stones, etc., by their size. They typically have a cylindrical or regular polygonal cross section and include a frame structure supporting either a single screen unit conforming to the frame structure or individual panel sections attached to the frame structure and to each other. Representative examples of such rotating sizers can be found in U.S. Pat. No. 779,149 to Cross; U.S. Pat. No. 1,284,669 to Haug; U.S. Pat. No. 1,427,031 to Stepp; U.S. Pat. No. 2,204,835 to Traylor; U.S. Pat. No. 4,184,944 to Tytko; U.S. Pat. No. 4,222,865 to Valeri et al.; U.S. Pat. No. 4,670,136 to Schmidt et al.; U.S. Pat. No. 5,049,262 to Galton et al.; U.S. Pat. No. 5,213,217 to Galton et al.; and U.S. Pat. No. 5,346,071 to Page et al. The single wrap around screen has the advantage of being fairly easy to attach to the frame structure. They present a problem however in that as the rotating load within the sizer shifts with the rotation thereof, the screen is constantly flexing downwardly. Since the screen is often attached only along its two longitudinal edges to each other and along its circumferential edges to the frame structure, the load carried by the screen causes cracking along the circumferential edges thereof. That is, as the trommel was rotated, the screen would continuously deform with each revolution thereof, leading to life cycle fatigue and cracking along the attached circumferential edges. To avoid this loading problem and the life cycle fatigue caused thereby, many of the devices disclosed in the prior art have utilized a screen panel construction. This reduces the prior art loading problem, but the sizer constructions disclosed therein are complex and difficult to construct.
It would be desirable to have a sizer or trommel that utilizes multiple screen panels to reduce the fatigue caused by the rotating load but that is simpler in construction and costs less to build than the prior art structures.